1. Field of the Disclosure
The present disclosure relates generally to an interference cancellation method of user equipment in a cellular communication system, and more particularly to an interference cancellation method on a basis of interference parameters that are blind-detected in a network-assisted interference cancellation and suppression (NAICS) system.
2. Description of the Related Art
In order to satisfy strict requirements of International Telecommunication Union Radio (ITU-R) Communication Sector next generation cellular networks, such as long term evolution advanced (LTE-A), which support a wide bandwidth up to 100 MHz through higher-order spatial multiplexing to eight layers and four layers in a downlink (DL) and an uplink (UL), respectively, and carrier aggregation (CA), have been designed.
It is noteworthy that spatial frequency reuse for using more cells may provide more capacity benefits than a single cell that with an increased spatial dimension or spectrum bandwidth. Therefore, heterogeneous networks, which use small cells in a macro cell environment, are increasingly being viewed as a promising path for the next generation cellular networks.
The heterogeneous networks above may provide various benefits, but the heterogeneous networks may cause the cellular network to face unprecedented challenges. Particularly, interference management, which is a major concern as the number of base stations (BS) increases, may increase considerably. In this context, advanced co-channel interference aware signal detection has drawn the attention of researchers in the course of the recent development of LTE-A systems.
Features of network-assisted interference cancellation and suppression (NAICS) are being researched by the 3rd Generation Partnership Project (3GPP). User equipment (UE) may perform interference cancellation on the assumption that interference parameters including a rank indicator (RI), a preceding matrix indicator (PMI), and a modulation (MOD) level have been known to the UE through network signaling.
Inclusion of a work item referred to as the NAICS in LTE Release 12 is currently under consideration. A study has obviously showed that a considerable performance benefit can be attained on the assumption that the interference parameters have been known to the UE by broadcasting {e.g., upper layer signaling such as radio resource control (RRC)}, or dedicated signaling {e.g., newly defined downlink control information (DCI)}.
However, since the back-haul capacity between the BSs, and the control channel capacity from the BS to the UE are generally limited, the assumption is not always applied to actual systems. In fact, interference cancellation technology between similar cells, which is known as further enhanced inter-cell interference coordination (FeICIC), has been well developed, focusing on pilot signals, i.e., cell-specific reference signals (CRS). Since the CRS interference cancellation (IC) requires only semi-static interference parameters, such as a physical cell identity (CID), CRS antenna ports (AP), and a multicast broadcast single frequency network (MBSFN) subframe configuration, it is noteworthy that signaling overhead enabling the FeICIC can be managed.
However, unlike the FeICIC, the NAICS addresses interference in a data channel, which is known as a physical downlink shared channel (PDSCH), and requires the knowledge about dynamic interference parameters including an RI, a PMI, and an MOD. The success of the NAICS on the basis of signaling depends on the interference BSs that use a group of the RI, the PMI, and the MOD, which are signaled, and this may potentially limit the scheduling flexibility of nearby cells.
In order to overcome the defects, such as the scheduling limitation and the network signaling overhead, the UE may blind-estimate the interference parameters from received signals. The maximum likelihood (ML) estimation, which includes exhaustive search among the available combinations of the RIs, the PMIs, and the MODs designated in the LTE system, is applied to joint blind detection (BD) of the RI, the PMI, and the MOD. The allocated RI, PMI, and MOD may be changed from one transmission time interval (TTI) to another TTI in the time area, and from one resource block (RB) to another RB in the frequency area over the UE devices, which are simultaneously scheduled, in LTE-orthogonal frequency division multiple access (LTE-OFDMA) systems. This indicates that the joint blind detection should be conducted with respect to each RB of all TTIs in the LTE DL systems.
However, since the interference parameters may be dynamically changed from one RB to another RB in the frequency area in every TTI, according to the channel condition, this assumption may limit the performance of scheduling and may cause an excessive increase in the network signaling load.